Hydrogen-bond enhanced thermal energy transport at functionalized, hydrophobic and hydrophilic silica–water interfaces

doi:10.1016/j.cplett.2009.06.052

Chemical Physics Letters

Volume 476, Issues 4–6, 16 July 2009, Pages 271-276

https://doi.org/10.1016/j.cplett.2009.06.052 Get rights and content

Abstract

In this Letter, we investigate the nanoscale heat transfer across hydrophilic silanol and hydrophobic silane interfaces. We calculate the thermal conductance at the interface via the vibrational relaxation of silica in aqueous solutions. Additionally, we directly determine the heat flux across the interface by non-equilibrium molecular dynamics. The results indicate a temperature and time dependence of the thermal conductance across the hydrophilic interface, whereas the conductance at the hydrophobic one stays constant, emphasizing the importance of hydrogen-bonded networks. Most importantly, we observe a rectifying effect of the hydrophilic silanol to the bulk substrate depending on the heat current direction.

Graphical abstract

Nanoscale heat transfer across amphiphilic silica wafers in water. The thermal conductance at the interface via the vibrational relaxation and via direct determination is calculated.

Introduction

Understanding heat transport across atomic-scale solid–liquid interfaces is important because the influence of surface atoms on heat transfer can be large in novel, designed nanoscale materials in engineering [1], [2], [3] and biophysical applications [4]. The Kapitza resistance R_th defines the thermal impedance between different materials. For nanoscale solid–liquid interfaces there is the additional contribution of the surface chemistry that may strongly influence the diffusion of heat in the surrounding liquid [2]. This is why, for example, highly conductive nanoparticles added to a fluid may significantly increase the overall thermal conductivity of the resulting nanofluid [5]. A large effect of the surface chemistry and wettability on cross-interfacial heat transfer were reported recently both numerically [6], [7], [8], [9], [10], [11] and experimentally [2], [3], [12]. Models only considering van der Waals interactions [6], [9] are not appropriate for drawing reliable conclusions on the heat transfer across hydrophilic water-based suspensions [3], [13]. Patel et al. [14] studied the heat transfer at water–surfactant interfaces, and showed a clear influence of H-bonds on the thermal conductance G = 1/R_th. Murad and Puri [10], [11] were focusing on the heat transfer between water and silica and water and silicon, respectively, but modeled the interfaces between these using classical Lorentz–Berthelot mixing rules neglecting possible effects due to hydrogen bonds across the interface.

The present Letter concentrates on the topic of interfacial conductance including the effects of surface chemistry, strength of cross-interfacial atomic (hydrogen) bonding, atomic vibrations, and density. The work demonstrates that a significantly larger, but temperature dependent thermal conductance occurs across the hydrophilic interface (silanol) than across the hydrophobic interface (silane) of a silica slab surrounded by water. Most importantly, comparing the different heat flow directions across an amphiphilic (one side hydrophobic and the other hydrophilic) silica slab, we observe a rectification effect in the hydrophilic thermal conductance. It is considerably lower when the heat is transmitted across the silane interface through the slab and toward the adjacent water, than the other way around. In addition, we find a significant difference in the thermal conductance values when comparing the obtained values from steady-state calculations, to those of transient calculations.

Section snippets

Problem definition and methods

The system of interest is defined in Fig. 1a, middle slab denoted with ‘F’ (floating). It is an ‘amphiphilic’ silica slab surrounded by water It’s left side is hydrophobic, functionalized with a silane Si–H monolayer, and its right side hydrophilic, functionalized with a silanol Si–OH monolayer. Two more amphiphilic substrates of the same type, one at each side of the ‘F’ slab of interest are embedded in the water domain as well (see Fig. 1a). Their purpose will be discussed in the sequel.

Results

Fig. 1b shows the radial distribution function (RDF) of water with a peak at ≈2.88 Å, in good agreement with the experimentally found O⋯O spacing in liquid water calculations underlying the good structural properties of TIP3P water [19]. The O⋯O and the O⋯H spacing between the hydrophilic silanol end (Si–OH) and the water molecules are 2.95 and 1.97 Å, respectively, i.e., slightly larger (≈5%) than corresponding values from recent density functional theory (DFT) [20]. It is evident that the O⋯O

Discussion

We selected silica since it is an important dielectric in the semiconducting industry. Due to the future needs of chip cooling with liquids, silica may become an important candidate for the study of direct liquid chip cooling. Also, from a physical point of view, silica has a thermal conductivity similar to water and therefore allows for a better understanding of the sole influence of hydrophilic or hydrophobic interfaces. Our results indeed show large conductance values at the hydrophilic

Conclusion

In this study, we presented results for the thermal conductance at hydrophobic silane (Si–H) and hydrophilic silanol (Si–OH) terminated interfaces of a silica slab submerged in water. The thermal exchange across the interfaces was investigated both via transient molecular dynamics by determining the thermal conductance via vibrational relaxation of silica immerged in water, as well as directly (NEMD) by determining the temperature discontinuity at the solid–liquid interface.

We showed an

References (25)

L. Xue et al.
Int. J. Heat Mass Transf.
(2004)
S. Murad et al.
Chem. Phys. Lett.
(2008)
Z. Wang et al.
Science
(2007)
P.A.E. Schoen et al.
Appl. Phys. Lett.
(2007)
O.M. Wilson et al.
Phys. Rev. B
(2002)
Z. Ge et al.
Phys. Rev. Lett.
(2006)
D. Ma et al.
Chem. Mater.
(2006)
X.F. Zhou et al.
J. Appl. Phys.
(2006)
S. Shenogin et al.
J. Chem. Phys.
(2006)
H. Kim et al.
Phys. Rev. B
(2005)

G. Balasubramanian et al.

J. Appl. Phys.

(2008)

S. Murad et al.

Appl. Phys. Lett.

(2008)

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Hydrogen-bond enhanced thermal energy transport at functionalized, hydrophobic and hydrophilic silica–water interfaces

Abstract

Graphical abstract

Introduction

Section snippets

Problem definition and methods

Results

Discussion

Conclusion

Int. J. Heat Mass Transf.

Chem. Phys. Lett.

Science

Appl. Phys. Lett.

Phys. Rev. B

Phys. Rev. Lett.

Chem. Mater.

J. Appl. Phys.

J. Chem. Phys.

Phys. Rev. B

J. Appl. Phys.

Appl. Phys. Lett.